Determination of ↑(226)Ra in Mineral Drinking Waters by αLiquid Scintillation with Rejection Of β-γ Emitters

摘要

The radiotoxicity of radium isotopes (especially the long-half-life ↑(226)Ra requires their monitoring in drinking or nuclear wastes. We studied the applicability of the PERALS method of detection (photon electron rejecting αliquid scintillation) for radium measurement. This method combines a liquid scintillation with pulse shape analysis for β rejection and specific chemical extractants included in the scintillating cocktail. Radium is separated by an extractive-scintillator cocktail called RADAEX containing 2-methyl-2-heptylnonanoic acid (HMHN) and dicyclohexano-21-crown-7 (Cy↓(2)21C7) as extractant molecules. The variation of the radium extraction has beenstudied relative to pH, salt concentrations, anion and cation effects, and the volume ratio between aqueous and organic phases. The main parameter affecting the radium extraction in mineral drinking water is its complexation by inorganic anions, especially sulfate. Due to the lack of thermodynamic data, some complexation constants had to be determined. For instance, the value reported in this paper for radium sulfate (logβ = 2.58 ±0.22) is in good agreement with that from the literature. The knowledge of complexation constants allows the determination of radium extraction recovery for any solution when the inorganic anion concentrations had been measured by capillary zone electrophoresis. The detection limit for this technique is found to be equal to 0.006 Bq·L↑(-1) using only 6 mL of sample solution for analysis. Several French mineral waters have been studied and the results compared with determinations of uranium and thorium concentrations by ICPMS and time-resolved laser induced fluorescence (TRLIF).